A proposal for broadband wavelength conversion using four-wave mixing is presented based on a slot waveguide with silicon nanocrystals (Si-nc’s) as the optical nonlinear material. The dispersion of the waveguide is engineered to realize a flat dispersion as well as a small effective mode area for better nonlinear interaction by optimizing the waveguide dimensions. The conversion performance is synthetically analyzed and numerical results show that a bandwidth of over $400\mathrm{nm}$ and an efficiency of $-2.38\mathrm{dB}$ can be achieved using a pump power of $150\mathrm{mW}$ in a $4\mathrm{mm}$ long Si-nc slot waveguide with slot width of $50\mathrm{nm}$, slab width of $310\mathrm{nm}$, and height of $305\mathrm{nm}$.

A reconfigurable dual-channel all-optical logic gate is proposed and experimentally demonstrated using four-wave mixing in a silicon waveguide for polarization encoding signals. Six logic functions, XNOR, AND, NOR, XOR, $A\overline{B}$, and $\overline{A}B$ are implemented at two different wavelength channels by adjusting the polarization states of two 10 Gb/s non-return-to-zero polarization-shift keying (NRZ-PolSK) signals modulated by 10-bit on–off keying (OOK) sequences. The eye diagrams of the logic signals are clearly observed, and the logic functions are well demonstrated as the two incident NRZ-PolSK signals are both modulated by the OOK sequences, which originate from $2^{31}-1$ pseudo-random binary sequences.

All-optical wavelength conversion for mode-division multiplexing (MDM) signals is theoretically demonstrated by using the four-wave mixing (FWM) effect in a dual-mode fiber. The theoretical model is analyzed for FWM processes between a signal with two MDM channels (${\mathrm{LP}}_{01}$ and ${\mathrm{LP}}_{11}$ modes) and a pump with ${\mathrm{LP}}_{01}$ and ${\mathrm{LP}}_{11}$ modes. A method is presented to realize mode-preserving wavelength conversion by simultaneously converting the two signal mode channels to the corresponding idler modes with low crosstalk. The required dispersion performance of the dual-mode fiber is determined, and the fiber structure is optimized to support the MDM wavelength conversion. The 3 dB MDM conversion bandwidth is predicted to be as broad as 69.3 nm with a conversion efficiency of $-4.7\mathrm{dB}$ in a 200-m-long dual-mode fiber.

A comprehensive multiparameter model is proposed for underwater wireless optical communication (UWOC) channels to integrate the effects of absorption, scattering, and dynamic turbulence. The simulation accuracy is further improved by the combined use of the subharmonic method and the strict sampling constraint method by comparing the phase structure function with the theoretical value. The average light intensity and scintillation index are analyzed using the channel parameters of absorption, scattering, turbulence, flow velocity, and transmission distance. Under weak or medium turbulence, the bit error rate (BER) performance can be effectively improved by increasing the transmitting light power. The power penalty of a 50 m UWOC channel is 5.8 dBm from pure seawater to ocean water and 1.0 dBm from weak turbulence to medium turbulence, with the BER threshold of 10⁻⁶.

A proposal for polarization-independent wavelength conversion is presented based on four-wave mixing in a silicon nanowire waveguide using an angled-polarization pump. The principle of polarization independence is introduced and the theoretical model is established. The optimized incident pump polarization angle is obtained for different waveguide geometries, and a polarization-independent bandwidth of 64 nm is achieved with the efficiency fluctuation of less than 1 dB in a 285 nm × 650 nm silicon waveguide. The polarization-independent bandwidth is limited by the larger one of the TE- and TM-mode phase mismatches, and can be enhanced further by carefully tailoring the dispersion characteristics of the silicon nanowire waveguide.

We report an all-optical multiple-channel exclusive OR (XOR) gate for $10\text{\hspace{0.17em} Gbits}/\mathrm{s}$ non-return-to-zero differential phase-shift keying (NRZ-DPSK) signals using nondegenerate four-wave mixing in a silicon waveguide. The function of the logic XOR gate is experimentally demonstrated using $40\mathrm{bit}$ DPSK sequences. Also, the eye diagram of the XOR signal is clearly observed as the incident signals are both modulated by DPSK sequences originating from $2^{31}–1$ pseudorandom binary sequences.